const tween = {
  easeInQuad: function(pos){
      return Math.pow(pos, 2);
  },

  easeOutQuad: function(pos){
      return -(Math.pow((pos-1), 2) -1);
  },

  easeInOutQuad: function(pos){
      if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,2);
      return -0.5 * ((pos-=2)*pos - 2);
  },

  easeInCubic: function(pos){
      return Math.pow(pos, 3);
  },

  easeOutCubic: function(pos){
      return (Math.pow((pos-1), 3) +1);
  },

  easeInOutCubic: function(pos){
      if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,3);
      return 0.5 * (Math.pow((pos-2),3) + 2);
  },

  easeInQuart: function(pos){
      return Math.pow(pos, 4);
  },

  easeOutQuart: function(pos){
      return -(Math.pow((pos-1), 4) -1)
  },

  easeInOutQuart: function(pos){
      if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,4);
      return -0.5 * ((pos-=2)*Math.pow(pos,3) - 2);
  },

  easeInQuint: function(pos){
      return Math.pow(pos, 5);
  },

  easeOutQuint: function(pos){
      return (Math.pow((pos-1), 5) +1);
  },

  easeInOutQuint: function(pos){
      if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,5);
      return 0.5 * (Math.pow((pos-2),5) + 2);
  },

  easeInSine: function(pos){
      return -Math.cos(pos * (Math.PI/2)) + 1;
  },

  easeOutSine: function(pos){
      return Math.sin(pos * (Math.PI/2));
  },

  easeInOutSine: function(pos){
      return (-.5 * (Math.cos(Math.PI*pos) -1));
  },

  easeInExpo: function(pos){
      return (pos==0) ? 0 : Math.pow(2, 10 * (pos - 1));
  },

  easeOutExpo: function(pos){
      return (pos==1) ? 1 : -Math.pow(2, -10 * pos) + 1;
  },

  easeInOutExpo: function(pos){
      if(pos==0) return 0;
      if(pos==1) return 1;
      if((pos/=0.5) < 1) return 0.5 * Math.pow(2,10 * (pos-1));
      return 0.5 * (-Math.pow(2, -10 * --pos) + 2);
  },

  easeInCirc: function(pos){
      return -(Math.sqrt(1 - (pos*pos)) - 1);
  },

  easeOutCirc: function(pos){
      return Math.sqrt(1 - Math.pow((pos-1), 2))
  },

  easeInOutCirc: function(pos){
      if((pos/=0.5) < 1) return -0.5 * (Math.sqrt(1 - pos*pos) - 1);
      return 0.5 * (Math.sqrt(1 - (pos-=2)*pos) + 1);
  },

  easeOutBounce: function(pos){
      if ((pos) < (1/2.75)) {
          return (7.5625*pos*pos);
      } else if (pos < (2/2.75)) {
          return (7.5625*(pos-=(1.5/2.75))*pos + .75);
      } else if (pos < (2.5/2.75)) {
          return (7.5625*(pos-=(2.25/2.75))*pos + .9375);
      } else {
          return (7.5625*(pos-=(2.625/2.75))*pos + .984375);
      }
  },

  easeInBack: function(pos){
      var s = 1.70158;
      return (pos)*pos*((s+1)*pos - s);
  },

  easeOutBack: function(pos){
      var s = 1.70158;
      return (pos=pos-1)*pos*((s+1)*pos + s) + 1;
  },

  easeInOutBack: function(pos){
      var s = 1.70158;
      if((pos/=0.5) < 1) return 0.5*(pos*pos*(((s*=(1.525))+1)*pos -s));
      return 0.5*((pos-=2)*pos*(((s*=(1.525))+1)*pos +s) +2);
  },

  elastic: function(pos) {
      return -1 * Math.pow(4,-8*pos) * Math.sin((pos*6-1)*(2*Math.PI)/2) + 1;
  },

  swingFromTo: function(pos) {
      var s = 1.70158;
      return ((pos/=0.5) < 1) ? 0.5*(pos*pos*(((s*=(1.525))+1)*pos - s)) :
      0.5*((pos-=2)*pos*(((s*=(1.525))+1)*pos + s) + 2);
  },

  swingFrom: function(pos) {
      var s = 1.70158;
      return pos*pos*((s+1)*pos - s);
  },

  swingTo: function(pos) {
      var s = 1.70158;
      return (pos-=1)*pos*((s+1)*pos + s) + 1;
  },

  bounce: function(pos) {
      if (pos < (1/2.75)) {
          return (7.5625*pos*pos);
      } else if (pos < (2/2.75)) {
          return (7.5625*(pos-=(1.5/2.75))*pos + .75);
      } else if (pos < (2.5/2.75)) {
          return (7.5625*(pos-=(2.25/2.75))*pos + .9375);
      } else {
          return (7.5625*(pos-=(2.625/2.75))*pos + .984375);
      }
  },

  bouncePast: function(pos) {
      if (pos < (1/2.75)) {
          return (7.5625*pos*pos);
      } else if (pos < (2/2.75)) {
          return 2 - (7.5625*(pos-=(1.5/2.75))*pos + .75);
      } else if (pos < (2.5/2.75)) {
          return 2 - (7.5625*(pos-=(2.25/2.75))*pos + .9375);
      } else {
          return 2 - (7.5625*(pos-=(2.625/2.75))*pos + .984375);
      }
  },

  easeFromTo: function(pos) {
      if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,4);
      return -0.5 * ((pos-=2)*Math.pow(pos,3) - 2);
  },

  easeFrom: function(pos) {
      return Math.pow(pos,4);
  },

  easeTo: function(pos) {
      return Math.pow(pos,0.25);
  },

  linear:  function(pos) {
      return pos
  },

  sinusoidal: function(pos) {
      return (-Math.cos(pos*Math.PI)/2) + 0.5;
  },

  reverse: function(pos) {
      return 1 - pos;
  },

  mirror: function(pos, transition) {
      transition = transition || tween.sinusoidal;
      if(pos<0.5)
          return transition(pos*2);
      else
          return transition(1-(pos-0.5)*2);
  },

  flicker: function(pos) {
      var pos = pos + (Math.random()-0.5)/5;
      return tween.sinusoidal(pos < 0 ? 0 : pos > 1 ? 1 : pos);
  },

  wobble: function(pos) {
      return (-Math.cos(pos*Math.PI*(9*pos))/2) + 0.5;
  },

  pulse: function(pos, pulses) {
      return (-Math.cos((pos*((pulses||5)-.5)*2)*Math.PI)/2) + .5;
  },

  blink: function(pos, blinks) {
      return Math.round(pos*(blinks||5)) % 2;
  },

  spring: function(pos) {
      return 1 - (Math.cos(pos * 4.5 * Math.PI) * Math.exp(-pos * 6));
  },

  none: function(pos){
      return 0
  },

  full: function(pos){
      return 1
  }
}

export default tween;
